§ 1. Differentiation and Integration.—The lower we descend in the scale of animal life, the more important is sensation; the higher we mount, the more important is perception, in other words, the intrinsic intensity and feeling-tone of sensation counts for less; its meaning counts for more. The reaction which it sets up is directed not so much to the maintenance or removal of the present stimulation as to the attainment of remoter ends.

This graduated difference in the relative prominence of sensation and perception is accompanied and manifested by a corresponding variation in the nature of sense-experience itself. The more developed is perceptual consciousness the more delicately differentiated is sense-experience. In other words, there is a finer correspondence between differences in the nature of the external stimulus, and differences in the sensation produced. With this finer differentiation is connected more definite restriction. The more delicately discriminated sensations are, the more capable they are of coexisting simultaneously in the same consciousness without mutual interference or amalgamation. "Colours," says Dr. Ward, "are with us so distinct from sounds that—except as regards the drain upon attention—there is nothing in the intensest colour to affect the simultaneous presentation of a sound. But, at the beginning, whatever we regard as the earliest differentiation of sound might have been incopresentable with the earliest differentiation of colour, if sufficiently diffused, just as now a field of sight all blue is incopresentable with one all red. Or, if the stimuli appropriate to both were active together, the resulting sensation might have been what we should describe as a blending of the two, as purple is a blending of red and violet."* Thus "increased differentiation seems to be intimately connected with increased 'restriction.' "+ With differentiation and restriction there is loss of the intensity and of the intrinsic pleasantness or painfulness of the sensation itself. The intensity and feeling-tone of sensation need to be strongly emphasised, where the reaction depends directly on the mere existence of the sensation, as such. In so far as the reaction depends on the meaning of the sensation, and not on its mere existence, the important point is that its special quality should correspond accurately to the special quality of the stimulus. Any direct effect produced by its own intrinsic intensity and feeling-tone would interfere with its value as a vehicle of meaning—as an indication of something beyond its own existence. Thus, as perceptual consciousness becomes relatively more prominent and important, sensation is more delicately differentiated, more definitely restricted, less intense, and less strongly toned in the way of pleasure or pain.

* Article "Psychology," Encyclop. Brit., ninth ed., part xx., p. 46. + Ibid.